1. Field of the Invention
The present invention relates to a touch screen device that determines whether a pointing device for a touch operation is a pen or a finger.
2. Description of Related Art
A touch screen device is widely used in the fields of personal computers or handheld terminals. In addition, the touch screen device can be used as an interactive white board, by combining the touch screen device with a large screen display device, to be used in a presentation or a lecture for a large audience. In particular, such a use of the touch screen device is expected in the educational field, such as a school.
There are various touch screen devices that employ different principles to detect a touch position. For example, in a capacitive touch screen device, in which a plurality of electrodes are arranged in a panel to detect a change in capacitance in response to a touch operation with a pointing device, such as a finger, or the like, an amount of calculation necessary to obtain a touch position increases, as the number of electrodes increases. In particular, when the touch screen device is used as an interactive white board, the number of electrodes increases as the size of the touch screen device increases. Thus, the amount of calculation necessary to obtain a touch position increases by a large amount.
When the processing capacity of a controller is insufficient to handle such an increase in the amount of calculation, a detection process of a touch position cannot follow touch operations using a pointing device, such as a finger. Accordingly, for example, operation feeling may be deteriorated in a handwriting mode, in which a line is drawn along a trajectory of the pointing device when a user moves the pointing device. In view of such a situation, a controller having a high processing capacity may be employed. However, this increases a manufacturing cost significantly, and there is a limit to acceleration of the processing speed.
The calculation load of the controller may be reduced by increasing an arrangement interval between electrodes to reduce the number of electrodes. However, in a process to detect a touch position, the touch position is detected based on the change in signals output from the electrodes in response to a touch operation. The amount of change in the signals decreases as the distance between the touch position and the electrode increases. Accordingly, when the arrangement interval between electrodes increases, an accuracy of detection of touch position may be reduced. In view of this, a technology is known that increases the accuracy of the detection of the touch position by correcting the amount of change in signals in response to a touch operation (Related Art 1).
Further, when different properties (or functions), such as a color of drawing and the like, are set for a pen and a finger, such that the pen and the finger can be used in different manners, convenience can be improved. In order to do so, however, it is necessary to determine whether the pointing device used in a touch operation is a pen or a finger. With respect to the determination of the pointing device, a technology is known in which a pen is discriminated from a finger according to a contact area of a pointing device on a touch surface (Related Art 2).
However, when the amount of change in signals in response to a touch operation is extremely small due to a large distance between the touch position and an electrode resulting from increasing the arrangement interval between electrodes, an accuracy of determination of the pointing device is reduced. In particular, when a touch screen device is used as an interactive white board, the arrangement interval between electrodes should be significantly large relative to the finger size, and thus, it is difficult to secure the accuracy of determination of pointing device.    Related Art 1: Japanese Patent Application Publication No. 2-109117    Related Art 2: Japanese Patent Application Publication No. 4-60715